Abstract: Using two-dimensional Langevin dynamics simulations, we investigate the kinetics of the bimolecular chemical reactions in crowded environments. An important finding is that the dependence of the mean reaction time τ on the area fraction of crowders  relies on the manner of varying . Specifically, When  is increased by adding crowders into the circular domain, a monotonic increase in τ is observed. Moreover, the growth rate of τ becomes much faster once the percolation occurs in the system. As  is tuned by varying the radius of the circular domain R, τ has a minimum as a function of , which is a result of two distinct dynamical regimes, i.e., the crowding-dominated regime and the density-dominated regime. As the size of crowders becomes larger, the reaction process is found to be accelerated. Finally, we show that distributions of the reaction time obey the exponential ones, and the degree of crowding does not alter the distribution pattern.